Bently Nevada 3300/40

Bently Nevada 3300/40

Product Overview The 3300/40 is a specialized monitor designed to measure shaft eccentricity, which is the slow-roll mechanical and electrical runout of a rotating shaft. This monitor utilizes two proximity probes to measure the peak-to-peak amplitude of shaft bow or bend during slow-roll conditions. Eccentricity monitoring is critical for large steam turbines and generators, where excessive shaft bow can cause severe vibration during startup or lead to rotor-to-stator contact. The 3300/40 provides early detection of shaft bow, misalignment, and foundation issues that contribute to eccentric rotation.

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Description

Bently Nevada 3300/40

Technical Specifications

Parameter Specification
Input Two proximity probe signals
Input Impedance 10 kΩ
Scale Factor 7.87 V/mm (200 mV/mil) on AISI 4140 steel target at 1.0 mm gap
Field Wiring 0.2–1.5 mm² (16–24 AWG), maximum length 305 m
Recorder Output 4–20 mA or 0 to -10 Vdc
Alarm Relays Dual relay alarm options (non-epoxy sealed)
Operating Temperature 0°C to +65°C
Dimensions 241.3 mm × 114.3 mm × 25.4 mm
Weight Approximately 0.45 kg
Origin USA

Functional Features

  • Measures peak-to-peak shaft eccentricity during slow-roll conditions
  • Uses dual proximity probes for accurate bow detection
  • Provides early warning of shaft bow, misalignment, and foundation problems
  • Offers real-time recorder outputs for trending and analysis
  • Features dual relay alarm outputs for proactive maintenance
  • Includes front-panel display for direct eccentricity reading
  • Performs continuous transducer OK checking
  • Supports programmable alarm setpoints

Structural Characteristics The eccentricity monitor is constructed as a standard 3300 rack module with a front panel containing an LCD bargraph display, LED indicators, and programming switches. The unit accepts inputs from two proximity probes mounted 90 degrees apart around the shaft circumference. The internal signal processing circuitry extracts the slow-varying DC component representing shaft bow from the dynamic vibration signal.

Working Principle During slow-roll operation (typically 100–500 RPM), two proximity probes mounted orthogonally on the bearing housing measure the distance to the shaft surface. As a bowed shaft rotates, the probe-to-shaft distance varies sinusoidally at the rotational frequency. The monitor extracts this slow-roll variation, filters out higher-frequency vibration components, and measures the peak-to-peak amplitude. This value represents the total indicated runout (TIR) or eccentricity of the shaft. The monitor compares this value against alarm thresholds to warn operators of excessive bow before attempting full-speed operation.

Installation Requirements

  • Install two proximity probes at 90-degree offset positions around the shaft
  • Mount probes at identical radial distances from the shaft centerline
  • Use shielded coaxial cable for all transducer connections
  • Ensure proper probe gap setting for linear range operation
  • Program alarm setpoints based on manufacturer slow-roll limits
  • Verify eccentricity measurement during known slow-roll conditions
  • Test alarm relay operation before placing in service

Application Scenarios

  • Large steam turbine slow-roll monitoring
  • Generator shaft bow detection
  • Compressor startup eccentricity measurement
  • Motor rotor bend assessment
  • Refinery critical equipment startup supervision
  • Power plant turbine supervisory instrumentation

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